This invention relates generally to the field of geophysical prospecting. More particularly, the invention relates to the field of cables and equipment for marine geophysical surveys.
In the oil and gas industry, geophysical prospecting is commonly used to aid in the search for and evaluation of subterranean formations. Geophysical prospecting techniques yield knowledge of the subsurface structure of the earth, which is useful for finding and extracting valuable mineral resources, particularly hydrocarbon deposits such as oil and natural gas. A well-known technique of geophysical prospecting is a seismic survey.
Marine geophysical surveying, such as seismic or electromagnetic surveying, is typically performed using sensor cables, such as “streamers” towed near the surface of a body of water or an “ocean bottom cable” or “node” disposed at or near the water bottom. A streamer is in the most general sense a cable towed by a vessel. The sensor cable has a plurality of sensors disposed thereon at spaced apart locations along the length of the cable. In the case of marine seismic surveying the sensors are typically hydrophones, but can also be any type of sensor that is responsive to the pressure in the water, or in changes therein with respect to time or may be any type of particle motion sensor, such as a velocity sensor or an acceleration sensor, known in the art. In the case of marine electromagnetic surveying, the sensors may be electrodes or magnetic field sensors. Irrespective of the type of such sensors, the sensors typically generate an electrical or optical signal that is related to the parameter being measured by the sensors. The electrical or optical signals are conducted along electrical conductors or optical fibers carried by the streamer to a recording system. The recording system is typically disposed on the vessel, but may be disposed elsewhere.
Unfortunately, marine organisms adhere to and then grow on nearly everything that is placed in water for significant periods of time, including towed or ocean bottom geophysical equipment. Marine growth is often pictured in terms of barnacles, but also includes the growth of mussels, oysters, algae, bacteria, tubeworms, slime, and other marine organisms.
Marine growth results in lost production time required to clean the geophysical equipment. In addition, marine growth speeds corrosion, requiring quicker replacement of equipment, and increases drag resistance, leading to increased fuel costs. Thus, the elimination, or the reduction, of marine growth will have a major beneficial effect on the cost of marine geophysical surveying. Hence, marine growth presents a significant problem for a geophysical vessel operation due to downtime caused by a need for its removal, equipment damage, reduced seismic data quality due to increased noise, increased fuel consumption, and exposure of the crew to dangers associated with a streamer cleaning operations.
Thus, a need exists for a system and a method for protecting geophysical equipment in marine geophysical surveys, especially sensor cables, from marine growth.
While the invention will be described in connection with its preferred embodiments, it will be understood that the invention is not limited to these. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents that may be included within the scope of the invention, as defined by the appended claims.